The present invention relates to an optical fiber connector, a ferrule for use in the optical fiber connector and a method for manufacturing the same.
Conventionally, as this type of optical fiber connector there is known that which is equipped with a ferrule which has a configuration as illustrated in FIG. 13 and which is prepared by injection molding.
The ferrule illustrated in FIG. 13 is constituted by a main body of the ferrule. In this main body 1 of the ferrule, from the injection molding time an entire fiber insertion hole 2 is provided slenderly in such a way as to have substantially the same diameter as that of an elemental optical fiber. When into this insertion hole 2 the elemental optical fiber is inserted from an inlet thereof, the elemental optical fiber is positioned, fixed, centered and retained by the fiber insertion hole 2 as a whole, whereby the elemental optical fiber is retained precisely.
As manufacturing process steps for manufacturing the ferrule illustrated in the same figure there are known a series of process steps 300 to 306 such as those illustrated in FIG. 14.
In a process step (molding) 300, there is molded as illustrated in FIG. 15(a) by injection molding or the like a ferrule blank 1--1 which becomes a base of the ferrule main body 1 (refer to FIG. 13). This ferrule blank 1--1 is formed cylindrically and is provided with a prepared hole 2-1 for optical fiber insertion in such a way that this prepared hole passes through the blank between both end faces thereof. It is to be noted that the prepared hole 21 is that which becomes a base of the fiber insertion hole 2.
In a process step (inside diameter polishing) 301, from the standpoint of achieving a reduction in the manufacturing time length, a plurality of the ferrule blanks 11, 1--1, - - - , are unified as a set, whereby all the prepared holes 2-1 are polished simultaneously (refer to FIG. 15(b)).
In this inside diameter polishing, an operation of passing a setting wire 13 into the prepared hole 2-1 and thereby setting a plurality of the ferrule blanks 1--1 onto the wire 13, an operation of filling into a cylindrical body (sheath) 15 a setting 14 that consists of a plurality of the ferrule blanks 1--1, 1--1, - - - and charging adhesive 16 such as solder, lac, etc. into this cylindrical body 15 and thereby performing positioning and fixing of the setting 14, and an operation of drawing off the wire 13 from the setting 14 are performed sequentially. Next, a polishing taper wire 12 (whose diameter dimension becomes large in the longitudinal direction and is fixed in the ending half portion) is inserted into the prepared holes 2-1 from the end face side of the cylindrical body 15. Thereafter, with the cylindrical body 15 being rotated about its axis, the taper wire 12 is drawn off therefrom axially and taken up onto a reel not illustrated while scattered abrasive grains 10 are sequentially being supplied and adhered onto the taper wire 12 immediately before the ferrule blank 1--1, to thereby polish the prepared hole 2-1. Supply and adhesion of the scattered abrasive grains 10 are performed such that liquid scattered abrasive grains 10 are applied onto the taper wire 12 or this taper wire 12 is immersed therein.
That is, the inside diameter polishing is performed with respect to the prepared hole which is not machined whatsoever after molding of the ferrule blank.
It is to be noted that after polishing the abrasive 16 is removed and all the ferrule blanks 1--1, 1--1, - - - are taken off from the cylindrical body 15.
In a process step (outside diameter grinding [centerless method]) 302, from the standpoint of removing the outside diameter machining allowance of the ferrule blank 1--1 with a high efficiency, the ferrule blank 1--1 having had its inside diameter polished is set on, for example, a centerless supporting apparatus to thereby grind the outside diameter portion 1-1c of this ferrule blank 1--1 with the use of no center (refer to FIG. 15(c)).
In a process step (end face grinding) 303, rough grinding is executed with respect to the both end faces 1-1a and 1-1b of the ferrule blank 1--1 (refer to FIG. 15(d)).
In a process step (outside diameter grinding [both center method]) 304, from the standpoint of correcting the eccentricity between the outside diameter of the ferrule blank 1--1 and the prepared hole 2-1 and thereby making the both coaxial with each other, an outside diameter portion 1-1c of the ferrule blank 1--1 is ground as illustrated in FIG. 15(e). In this outside grinding, the ferrule blank 11 is supported with one center being at each end face. This both center supporting is performed by causing center jigs 6 and 7 to abut from the both end face sides 1-1a and 1-1b of the ferrule blank 1--1 onto the prepared hole 2-1 and thereby causing the ferrule blank 1--1 to be supported from the both end face sides 1-1a and 1-1b.
In a process step (outside diameter polishing) 305, the outside portion 1-1c of the ferrule blank 1--1 is polished to be finished to a desired roughness (refer to FIG. 15(f)).
In a process step (end face machining) 306, machining such as machining of the end face of the ferrule blank 1--1 into a convex spherical surface is performed (refer to FIG. 15(g)).
The following is to be noted. In the process step (molding) 300, as illustrated in FIG. 16(a), at a time of injection molding of the ferrule blank 1--1, a stepped portion 17 is provided with respect to an inlet 2-1b of the prepared hole 2-1. As illustrated in FIG. 17, this stepped portion 17 is used temporarily as an abutment basis for the center jig 7 when performing the outside diameter grinding that is to be performed with the use of the grinder 12 in the succeeding step (outside diameter grinding [both center method]) 304. Accordingly, after the performance of the outside diameter grinding, from the standpoint of preventing flawing of the elemental optical fiber by the stepped portion 17, chamfering (refer to FIG. 16(b)), circular-arc configuration chamfering (refer to FIG. 16(c)) or the like is performed with respect to the prepared hole inlet 2-1b to thereby shave off the stepped portion 17 and thereby finish the prepared hole inlet 2-1b, i.e. fiber insertion hole 2 inlet into the configuration of a smooth bowl that has no angular portion.
On the other hand, the ferrule illustrated in FIG. 18 is that which has been constructed from the standpoint of reducing the amount of the fiber insertion hole 2 finish-machined with it in mind that at even only a large-depth portion (one end side) 2a of the fiber insertion hole 2 alone it is possible to perform positioning, fixing, centering and retention (precise retention) of the Elemental optical fiber sufficiently.
That is, in this ferrule, from the injection molding time, only the large-depth portion (one end side) 2a of the fiber insertion hole 2 is formed to a diameter that is substantially the same as that of the elemental optical fiber and the remaining portion thereof is formed to a diameter that is sufficiently larger than the diameter of the elemental optical fiber. When inserting the elemental optical fiber into this fiber insertion hole 2, the elemental optical fiber is positioned, fixed, centered and retained not by the whole fiber insertion hole 2 but by only the large-depth portion (one end side) alone.
However, the above-mentioned conventional ferrule has the following problems.
In the conventional ferrule that is illustrated in FIG. 13, since it is of a structure wherein positioning and fixing of the elemental optical fiber are performed by the entire fiber insertion hole 2, it becomes necessary to perform finish machining for positioning and fixing thereof with respect to the entire fiber insertion hole 2, with the result that the amount of the fiber insertion hole machined and the amount of machining time become large. This is followed by an increase in the length of time for manufacturing the ferrule, which results in that a longer period of time is needed for completion of manufacture of the optical fiber connector.
In addition, according to the conventional ferrule illustrated in this figure, the fiber insertion hole 2 is slender and an elongate small-diameter hole, and therefore at the injection molding time curving of the fiber insertion hole 2 occurs, with the result that a step for correcting this curving becomes additionally needed separately. Further, from the standpoint of preventing flawing of the elemental optical fiber, it is necessary to perform a secondary machining such as chamfering, circular-arc configuration chamfering with respect to the inlet of the fiber insertion hole 2. Therefore, in this respect also, the manufacturing process steps for manufacturing the optical fiber connector increase in number, with the result that a larger amount of time is needed for completion of the manufacture thereof, which results in an increase in the manufacturing cost.
In the conventional ferrule illustrated in FIG. 18, as illustrated in FIG. 19, at the time of grinding the outside diameter the contact of the center jig 7 with the other end 2b of the fiber insertion hole 2 is unstable. The reason for this is that since the other end 2b of the fiber insertion hole 2 that is abutted against by the center jig 7 is as is immediately after having been injection molded, the contour thereof has a number of concavities and convexities and therefore the hole precision at the other end 2b of the fiber insertion hole is low. This causes deterioration in the precision of the outside diameter grinding (the circularity of the outside diameter of the ferrule, the coaxiality of the outside diameter of the ferrule and the fiber insertion hole, etc.), which results in that it is not possible to obtain a highly precise optical fiber connector.
It is to be noted that in order to avoid such inconvenience, it can be also considered to perform a so-called "center-hole machining" of, before the performance of the outside diameter grinding, finishing the other end 2b of the fiber insertion hole to a prescribed dimensional precision. However, separate addition of this center hole machining causes additional increase in the number of the manufacturing process steps for manufacturing the optical fiber connector, with the result that a larger amount of time is needed for completion of the manufacture thereof, which results in an increase in the manufacturing cost.
Also, according to the conventional ferrule illustrated in FIG. 18, a stepped portion 18 exists at a large-depth portion side due to the difference in diameter between the large-depth side of the fiber insertion hole 2 and the remaining portion thereof. For this reason, when performing injection molding, blow holes occur in the stepped portion 18 and the portion in the vicinity thereof due to a rapid change in the sectional area involved therein, with the result that the positioning portion (the large-depth portion [one end 2a side] of the fiber insertion hole 2) located forwardly from the stepped portion 18 cannot be finished into a desired configuration. Therefore, the positioning, fixing, centering and retaining precision for the elemental optical fiber is inferior. For this reason, a high precision optical fiber connector cannot be obtained, which is accompanied by a decrease in the reliability of the optical communication. Also, burrs also are likely to occur in the stepped portion and these burrs cause damage to the elemental optical fiber. In this respect also, it is possible neither to obtain a high precision optical fiber connector nor to expect a highly reliable optical communication.
The above-mentioned ferrule manufacturing method has the following problems.
(1) In the conventional manufacturing process, as illustrated in FIG. 15(b), since the positioning and fixing of the ferrule blank 1--1 in the process step (inside diameter polishing) 301 are performed with the use of the adhesive 16, the operation of charging and setting the adhesive 16 that is to be performed as a preceding tooling for the performance of the inside diameter polishing and the operation of removing the adhesive 6 that is to be performed as a succeeding tooling are needed and in addition these operations must be performed by man power. Therefore, a larger amount of time is spent for performance of these tooling operations, which results in that the entire ferrule manufacturing time length increases. Therefore, a larger amount of time for completion of manufacture of the optical fiber connector is needed. On the other hand, full automation of the manufacturing process steps therefor is difficult.
Furthermore, in the above-mentioned polishing and fixing that are performed using the adhesive 16, the set condition of the ferrule blank 1--1 collapses due to shrinkage and the like of the adhesive 16, with the result that the ferrule blank 1--1 and prepared hole 2-1 are disadvantageously inclined with respect to the cylindrical body 15. In consequence, the setting precision decreases with the result that the matching conditions for performance of the inside diameter polishing deteriorates. For this reason, no desired machining precision is obtained. Further, the use of the adhesive 16 results in the collapse of the set condition as mentioned above and hence in the inferior balance of the cylindrical body 15 as a whole. Therefore, the high-speed rotation of the cylindrical body 15 is impossible to perform and the machining efficiency is impossible to increase.
(2) In the conventional manufacturing process, because the eccentricity and parallelism degrees between the prepared hole 2-1 formed by molding and the outside diameter of the ferrule blank are not those which are desired and because the inside diameter polishing that is to be performed in the process step 301 is performed with respect to the prepared hole 2-1 that is not machined whatsoever after molding and therefore the inside diameter polishing is performed independently of the outside diameter of the ferrule blank, after the inside diameter polishing no correction is made of the eccentricity and parallelism degrees between the prepared hole 2-1 and the outside diameter of the ferrule blank, with the result that the eccentric or inclined prepared hole 2-1 spreads as it is. For this reason, the outside diameter machining allowance of the ferrule blank 1--3 must be made unnecessarily large, with not only the eccentricity and inclination resulting from errors in the molding in the process step 300 but also the spread of the eccentric and inclined prepared hole 2-1 in estimation. As a result, a larger amount of time is needed for removal of such unnecessary machining allowance, which causes an increase in the total ferrule manufacturing time length, which necessitates the use of a larger amount of time for completion of the manufacture of the optical fiber connector. Also, an amount of molding material of the ferrule blank 1--3 that is larger by that extent becomes necessary. This causes an increase in the manufacturing cost of the optical fiber. Further, after the performance of the inside diameter polishing, the additional necessity arises of providing the process step 304 for removal of the above-mentioned inclination and eccentricity.
(3) According to the conventional manufacturing process, in the case where the outside diameter machining allowance of the ferrule blank 1--3 is large and in addition the both center supporting in the process step 304 is adopted as mentioned above, since the centering jig is small in thickness because of the prepared hole 2-1 being small in diameter, the machining efficiency is low. Therefore, the process step of removing the outside diameter machining allowance with a high efficiency becomes needed separately. In this sense, the outside diameter grinding that uses the centerless method, which provides an excellent machining efficiency, is adopted as the process step 302 between the process steps 301 and 304. However, since the centerless method is inferior in the ability of smallening the eccentricity, it is needed to set an air cut that corresponds to the eccentricity when machining in the process step 304 is performed. Therefore, the amount of machining time in the process step 304 cannot be largely shortened, with the result that the entire ferrule manufacturing time length is not shortened.
It is to be noted that although in order to correct the eccentricity of the prepared hole 2-1 it can be also considered to apply in the process step 302 the outside diameter grinding that uses the wire centerless method instead of the one which uses the centerless method, the adoption of such wire centerless method results in that a large amount of time is needed for the performance of the tooling operation such as the operation of setting the ferrule blank 1--3 on the wire. On the other hand, omitting the use of man power is difficult and therefore a rise in the manufacturing cost is unavoidable.
(4) In the conventional manufacturing process, when the prepared hole is of a configuration whose forward end is small in diameter such as a nozzle as illustrated in FIG. 18, due to the variation in the diameter of the prepared hole the ferrule blank 1--3 is inconveniently set in the process step 301 while being inclined with respect to the setting wire 13 as illustrated in FIG. 20, with the result that difficulties arise in setting the ferrule blank 1--3 with a high precision in parallel with the wire 13. As a result, the machining precision becomes more seriously deteriorated.